1. Field of the Invention
The present invention relates to display devices including a display screen constituted by a plurality of pixels. More specifically, the present invention relates to a display device which includes a display screen constituted by a plurality of pixels and which can be used in a liquid crystal display, a PDP (Plasma Display Panel), an organic EL (Electroluminescent) display, a FED (Field Emission Display), and the like.
2. Description of the Related Art
Various thin display devices such as a liquid crystal display, a PDP (Plasma Display Panel), an organic EL (Electroluminescent) display, and a FED (Field Emission Display) have been widely used as such a display device, recently. For these display devices, further improvement in performances is needed. For example, further reduction in size and improvement in resolution are needed for a liquid crystal display used in a cellular phone and the like. In order to satisfy such demands, the resolution needs to be increased without increasing an area of a display region. A method of reducing the size of a sub-pixel constituting a pixel and simultaneously increasing the number of pixels may be mentioned as a method of realizing such needs. However, a wiring for supplying image signals to sub-pixels constituting each pixel and a thin film transistor for driving the pixel need to be formed in one pixel. Therefore, if the size of the sub-pixel is reduced, the aperture ratio is reduced and sufficient brightness in the display screen can not be obtained. In this respect, there is room for improvement.
For this problem, a method of changing a sub-pixel arrangement in one pixel, thereby increasing an apparent resolution without increasing the number of pixels may be mentioned (for example, refer to Japanese Kokai Publication No. Hei-06-324649 and Japanese Kokai Publication No. 2004-152737). The resolution is generally proportional to the number of pixels, but the apparent resolution is determined by a brightness distribution in one pixel. The display device such as a liquid crystal display generally includes pixels constituted by three sub-pixels of red (R), green (G), and blue (B) as shown in FIG. 1A (for example, refer to Japanese Kokai Publication No. Hei-07-181472). In this case, the brightness distribution has one peak in one pixel, as shown in FIG. 1B.
In contrast, in the sub-pixel arrangement proposed in a conventional device, as shown in FIG. 2A, one pixel is constituted by four sub-pixels of red (R), green (G), blue (B), and green (G), and the brightness distribution has two peaks in one pixel, as shown in FIG. 2B. Accordingly, this one pixel is apparently equivalent to two pixels. That is, if one pixel is constituted by four sub-pixels of R, G, B, and G, the resolution that is 1.5 times that in one pixel constituted by three sub-pixels of R, G, and B can be apparently obtained even if the number of pixels is the same. However, if the sub-pixels of the respective colors having the same size are displayed at maximum brightness, white balance is shifted to the green side and the display quality is reduced because the number of the G sub-pixel in one pixel is two times that of the R or B sub-pixel. In such a respect, there is room for improvement in order to provide a display device displaying an image constituted by a pixel including four sub-pixels of R, G, B, and G.